Conventionally, it is well known that a measurement device includes a flowing amount sensor and a humidity sensor which are arranged in an intake duct through which an intake air flows, so as to measure a flowing amount and a humidity of the intake air.
According to JP2015-87196A, the measurement device includes a housing that supports the flowing amount sensor and protrudes toward an inner periphery of the intake duct, and the humidity sensor is arranged on a side surface of the housing.
However, in the above measurement device, a heat of an internal combustion engine is transmitted to the humidity sensor through the housing, and a temperature of the humidity sensor is increased. Therefore, the temperature of the humidity sensor is different from a temperature of the intake air, and a bad effect to a detection value of the humidity of the intake air is generated. Thus, it is necessary to prevent a heat transmission from the housing to the humidity sensor.
According to Japanese Patent No. 5445535, it is well known that an assembly supporting the humidity sensor is provided separately from the housing, and the assembly is separated from the housing and protrudes toward the inner periphery of the intake duct.
In the above measurement device, since the housing is separated from the assembly, the heat transmission from the housing to the humidity sensor can be prevented, and an increasing of the temperature of the humidity sensor can be suppressed.
However, according to Japanese Patent No. 5445535, since the assembly has a cross section that is perpendicular to a longitudinal direction of the assembly and is a rectangle shape, a pressure loss may generate relative to a flow of the intake air.
According to Japanese Patent No. 5445535, a humidity detection element is mounted to the measurement device, and the measurement device measures the flowing amount and the humidity of the intake air.
It is highly possible that the measurement device and the intake duct provided with the measurement device receive a heat of an engine room, and then a temperature of the measurement device and a temperature of the intake duct are increased.
Then, a heat of the measurement device and the intake duct is transmitted to the humidity detection element through a member supporting the humidity detection element or a connection portion that is electrical. In this case, the member may be a bypass housing, and the connection portion may be a lead pin.
As a result, the temperature of the humidity detection element is higher than the temperature of the intake air passing through an interior of the intake duct. When the temperature of the humidity detection element is different from the temperature of the intake air that is a measurement subject, the humidity of the intake air cannot be accurately measured by the humidity detection element.
According to WO2014/060161, a cover covers the humidity sensor.
In the measurement device according to WO2014/060161, the cover includes two openings arranged along a flowing direction of the intake air. The intake air flows into the cover through the opening that is placed at a upstream side of the other opening, passes through the measurement device, and returns to the intake duct through the opening that is placed at a downstream side.
According to WO2014/060161, the measurement device prevents a foreign matter from entering the cover so as to protect the humidity sensor. However, the measurement device cannot efficiently suppress the pressure loss.